I been looking at bromptons a bit too, basically there is one frame.
Each model has a three letter acronym, first says what style of handle bars, 2nd is number of gears (1,2,3 or 6) then the final one is whether you have no mudguards, mudguards or rear rack. Then there is the range of colours, lights and luggage fitments you can add on the brompton site.
Bike shops tend to have a few models for example evans only has one single speed model the m1e (high rise bars, singlespeed, no racks). Brompton themselves don’t do cycel2work so you’d have to go through a shop.